How to color terminal output with variable name in another variable

Question

So I want to color my terminal output but nothing works for me. I have script with code and txt file which I read input from. It looks something like this:

example.txt

                                    ${BLUE}_.
                            _/=\:<
                          .#/*${RED}let}
                        //as\@#:~/
                       try()|:-./
                      ${BLUE}*~let${RED}:>${BLUE}@{#
                      </>}#@~*/
                     ${RED}(+!:~/+/
                     /={+|
-

script.sh

BLUE="\033[0;34m"
RED="\033[0;31m"
# print example.txt but colored

I would only use this if you are absolutely sure that example.txt cannot contain malicious code: eval echo -e "$line" — Cyrus
– Cyrus, Commented Aug 8, 2022 at 20:55
This works with this example but it won't with my code because in actual txt file are lines that look like this: (@+_let#do/.@#=#>[/]#let=#or@\=<()~if)*<)\). It's not code just string code-styled and I don't want to run it just print it. — szym
– szym, Commented Aug 8, 2022 at 21:15
Do you want to output only one line at a time in your loop or do you want to do more? — Cyrus
– Cyrus, Commented Aug 8, 2022 at 21:16
please update the question to show more sample inputs that are more representative of your real files — markp-fuso
– markp-fuso, Commented Aug 8, 2022 at 21:25

Léa Gris · Accepted Answer · 2022-08-09 07:03:16Z

1

Very simply as:

BLUE=$'\033[0;34m' RED=$'\033[0;31m' envsubst < example.txt

By having the ANSI sequences directly in the environment variables, rather than escape codes, this relieves the need to un-escape the whole file content. ANSI sequences are already encoded.

Now, a more portable approach would be, to get the actual sequences from tput commands, rather than hard-coded ANSI.

BLUE=$(tput setaf 4) RED=$(tput setaf 1) envsubst < example.txt

edited Aug 9, 2022 at 7:03

answered Aug 8, 2022 at 22:17

Léa Gris

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Cyrus · Accepted Answer · 2022-08-08 21:40:08Z

1

With bash and envsubst:

export BLUE="\033[0;34m"
export RED="\033[0;31m"
printf "%b\n" "$(envsubst <example.txt)"

See: man envsubst

answered Aug 8, 2022 at 21:40

Cyrus

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2 Comments

szym Over a year ago

Works almost perfect! But is there a way to prevent it from escaping characters like \v or \n that may happen in example.txt or do I have to change \v to \\v in example.txt?

Léa Gris Over a year ago

@szym See my answer for how to not interpret back-slashes as escape sequences in the example.txt file.

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